1. Field of the Invention
The present invention relates to a method for estimating brain surface coordinates relating to measurement/stimulation in near-infrared spectroscopy (NIRS), a transcranial magnetic stimulator (TMS), and the other transcranial brain function measuring/stimulating methods; its software program; and a transcranial brain function measuring apparatus for displaying measuring/stimulating results using the brain surface coordinates estimated by the methods; and more particularly to a method for projecting measurement data developed on a head surface as arbitrary points on the head surface or its set onto a brain surface underlying the head surface to express them; the software program therefor; and an apparatus therefor.
2. Description of the Related Art
In order to find positions on brain surface being objects of measurement/stimulation in a transcranial brain function measuring/stimulating method, it is required to obtain a structural image of the brain in each case by using a brain imaging procedure such as an application of a nuclear magnetic resonance apparatus (MRI). However, such a brain imaging procedure is complicated, and specific equipment is required. Thus, a method for finding positional correspondences more easily between a head surface and its brain surface is desired.
Heretofore, such a study that positions at which electrodes are disposed on a head surface are intended to correlate to a brain surface structure underlying the head surface has been made in a field of brain wave study. The most typical method in the fields of research is a sphere fitting method (see Non-Patent Literatures 1 and 2). The sphere fitting method is the one wherein a brain surface and its head surface are applied to spheres each having the same center as that of the other. According to the sphere fitting method, when a radius of the sphere representing the head surface is designated by r1, while when a radius of the sphere representing the brain surface is designated by r2, an arbitrary point on the head surface may be expressed as a polar coordinate point (r1, φ, θ); and a brain surface point corresponding to the head surface point can be obtained by replacing r1 by r2.
The sphere fitting method is suitable for brain wave study. However, since non-spherical head surface and brain surface are applied to spheres in the sphere fitting method, there is a problem of an appearance of a spatial distortion. In brain wave studies, since a presumption of signal sources of brain waves is conducted with a low spatial resolution in a three-dimensional space, there is not a particular problem from a practical point of view, even if there is any deviance in correspondences between the brain surface and the head surface. In other transcranial brain function measuring/stimulating methods, however, a projective method having a higher spatial resolution is desired.
In even a case where a brain image exists as a result of an imaging procedure by means of MRI and the like, a basic manner for allowing arbitrary points on a head surface to be in response to points on the brain surface underlying the head surface has not yet been established, so that a development for a correct projection method is desired.
Non-Patent Literature 1: Towle, V. L, Bolanos, J., Suarez, D., Tan, K., Grzeszczuk, R, Levin, D. N., Cakmur, R, Frank, S. A. and Spire, J. P. 1993. The spatial location of EEG electrodes: locating the best-fitting sphere relative to cortical anatomy. Electroencephalogr. Neurophysiol. 86: 1-6.
Non-Patent Literature 2: Lagerlund, T. D., Sharbrough, F. W., Jack, C. R. Jr., Erickson, B. J., Strelow, D. C., Cicora, K. M. and Busacker, N. E. 1993. Determination of 10-20 system electrode locations using magnetic resonance image scanning with markers. Electroencephalogr. Clin. Neurophysiol. 86: 7-14.